This study represents an attempt to elucidate the structural and biochemical components involved in the final phases of secretion including membrane fusion and release of product. In the ciliated protozoa, Paramecium and Tetrahymena, our previous data indicate that the presence of a specific intramembrane particle array -- the fusion rosette -- is correlated with the site of secretory release (Satir, B., et al., 1973; Satir, B., 1974a). From studies on a unique series of secretory mutants of Paramecium tetraaurelia, we have shown that the rosette is an essential feature of the process of exocytosis in these systems. We are continuing to study the molecular events at the membrane level that govern the secretory process. Utilizing the secretory mutants of Paramecium, we will study the effect of temperature on assembly of the fusion rosette and the biochemical composition of the rosettes. We plan to analyze differences in SDS acrylamide gel patterns of pellicles from strains with the rosettes vs. without the rosettes. Using the well defined Tetrahymena system, we will attempt to develop an in vitro system of secretion. The ionic conditions necessary for secretion, i.e., stimulus-secretion coupling, will be examined in both protozoa using Ca ions ionophores. These findings will be extended to higher systems, such as the mast cell which we are examining in parallel to the protozoan systems.